Bian Xu (萹蓄) — Knotgrass | TCM Herb Guide
Key Takeaways
- Nature: Slightly Cold | Taste: Bitter
- Category: Herbs that Drain Dampness (Diuretic Herbs)
- Latin: Polygoni avicularis Herba
At a Glance
- Herb: Bian Xu
- Chinese name: 扁蓄 (Biǎn Xù)
- Latin name: Polygoni avicularis Herba
- Nature: Slightly Cold
- Taste: Bitter
- Meridian: Bladder
- Category: Herbs that Drain Dampness (Diuretic Herbs)
- Introduction: Bian Xu (萹蓄), Herba Polygoni Avicularis, is the dried aerial part of Polygonum aviculare, the common knotgrass found along roadsides and fields worldwide. It clears damp-heat from the lower jiao, promotes urination for painful dysuria, and kills intestinal parasites. Often combined with Qu Mai as a classic pair in Ba Zheng San. Modern pharmacology confirms avicularin and other flavonoids with diuretic, antimicrobial, and anthelmintic activity.
Action
- Clears damp-heat and promotes urination
- Relieves painful, difficult urination (lin syndrome)
- Kills parasites
- Stops itching (topical use)
Clinical Application
- Damp-heat lin syndrome: burning, painful, dark scanty urine — combines with Qu Mai, Hua Shi, Mu Tong
- Urinary tract infection with heat signs — combines with Huang Bai, Zhi Mu, Ze Xie
- Intestinal parasites: roundworms, pinworms — combines with Shi Jun Zi, Ku Lian Pi
- Vaginal itching and discharge from damp-heat — used as external wash
- Jaundice from damp-heat — combines with Yin Chen Hao, Zhi Zi
Precautions
- Dosage: 9–15 g in decoction; large doses for parasites
- Contraindicated in pregnancy
- Contraindicated in kidney deficiency without heat or cold patterns of the lower jiao
- Use cautiously in spleen deficiency
- External use is safe and effective for skin itching and vaginal infections
Formula
- Ba Zheng San (八正散): Bian Xu, Qu Mai, Hua Shi, Mu Tong, Che Qian Zi, Zhi Zi, Da Huang, Deng Xin Cao, Gan Cao — classic damp-heat dysuria formula
- Bian Xu Tang (萹蓄汤): Bian Xu, Huang Bai, Zhi Mu — clears lower jiao damp-heat
- External wash: Bian Xu decoction applied to perianal area or genitals for parasites and itching
Combinations
- Common Knotgrass (扁蓄) + Dianthus Herb (瞿麦) + Akebia Stem (木通) → Ba Zheng San (八正散): clear damp-heat; hot lin and dysuria and urinary tract infection
- Common Knotgrass (扁蓄) + Plantain Seed (车前子) + Talcum (滑石) → clear heat, promote urination; urinary gravel and stones
- Common Knotgrass (扁蓄) + Lightyellow Sophora Root (苦参) + Phellodendron Bark (黄柏) → clear damp-heat, kill parasites; genital itching
- Common Knotgrass (扁蓄) + Virgate Wormwood Herb (茵陈) + Gardenia Fruit (栀子) → clear damp-heat; jaundice with dark urine
- Common Knotgrass (扁蓄) + Quisqualis Fruit (使君子) + Melia Bark (苦楝皮) → expel intestinal parasites; abdominal pain from worms
Pharmacological Effects
- Diuretic; antibacterial
- broad spectrum
- Antiparasitic
- expels intestinal worms
- Anti-inflammatory; antifungal; hemostatic
- mild
- lowers blood pressure; promotes bile secretion
Classic Description
- Shen Nong Ben Cao Jing (《神农本草经》): ‘Governs spreading wet scabies and itching, abscesses and hemorrhoids, and kills the three parasites.’
- Ben Cao Gang Mu (《本草纲目》): ‘Common Knotgrass promotes urination, treats jaundice, and kills parasites.’
- Ming Yi Bie Lu (《名医别录》): ‘Treats female genital erosion, difficult urination, obstruction of bowel and urine; benefits the center and qi.’
- Ben Cao Bei Yao (《本草备要》): ‘Drains damp-heat, treats the five stranguries, kills parasites and stops itching; treats sores, scabies, and skin eczema.’